1. Field of the Invention
The present invention pertains to the technical field of purifying exhaust gas emissions from an internal combustion engine (also referred to hereinafter as “engine”). As it is used herein, the term “purify” refers to reducing the toxicity of the exhaust gases emitted by an internal combustion engine. More particularly, the present invention pertains to diagnosing whether there is any leakage by a flow path switching valve in an exhaust gas purifying system.
Exhaust gas is introduced into a bypass exhaust gas passage that includes a bypass catalytic converter. Preferably, the bypass exhaust gas passage is disposed relatively upstream of a main catalytic converter in a conventional exhaust system, and a flow path switching valve diverts the exhaust gas through the bypass exhaust gas passage after initiating a cold start-up of the engine.
2. Description of Related Art
Generally, exhaust gas cannot be sufficiently purified between the cold start-up of an internal combustion engine and the full activation of a catalytic converter, i.e., when the catalytic converter's temperature increases sufficiently. This is especially the case when a main catalytic converter is disposed a distance downstream from the engine (e.g., underneath an automobile). However, if the main catalytic converter is disposed closer to the engine, then the durability or lifespan of the catalyst can be significantly compromised due to thermal deterioration.
A related exhaust system includes a bypass exhaust gas passage and a bypass catalytic converter, which are disposed in parallel to an upstream portion of a main exhaust gas passage leading to a main catalytic converter. A flow path switching valve is configured to introduce the exhaust gas into the bypass exhaust gas passage immediately after initiating the cold start-up of the engine. As such, since the bypass catalytic converter is disposed upstream in the exhaust system relative to the main catalytic converter, it can be activated more rapidly to thereby allow purification of exhaust gas to begin sooner.
In the related exhaust system, when the flow path switching valve does not completely switch the flow path (e.g., exhaust gas leaks into the main exhaust gas passage when it is supposed to be prevented by the flow path switching valve), unpurified exhaust gas may be discharged to the atmosphere until the main catalytic converter is fully activated.
The related exhaust system includes a method for detecting flow rate reduction as a result of using the flow path switching valve; however, the related exhaust system fails to include anything in relation to diagnosing leakage of unpurified exhaust gas. Thus, there is a need for an apparatus that can properly diagnose leakage by the flow path switching valve.